The General Motors TH 350, introduced in 1969, was developed by Chevrolet and Buick. It was used in GM cars and trucks through 1984 with small-block engines. The TH400 transmission was first used in 1964 in Cadillac and Buick automobiles. The other GM brands got the TH400 in 1965. The TH400 was used in passenger cars through 1982 and trucks through the early 1990s. Both transmissions are noted for strength and durability but the TH400 is the stronger of the two. There are numerous aftermarket parts and complete units available from a host of suppliers.
Park the vehicle on a paved level surface and set the parking brake. Raise the front of the vehicle and support the front with jack stands.